Apparatus and process for preserving liquid carbon dioxide



1931- w'. J. EDMONDS ,835,699

APPWTUS AND PROCESS FOR PRESERVING LIQUID CARBON DIOXIDE Filed Oct. 10. 192? Patented Dec. 8, 1931 UNITED STATES, PATENT FFIcE WILLIAM J'. EDMONDS, OF TERRE HAUTE, INDIANA, ASSIGNOR TO COMMERCIAL SOLVENTS CORPORATION, OF TERRE HAU'IE, INDIANA, A CORPORATION OF MARY- LAND APPARATUS AND rnocnssron rrmsnnvme LIQUID CARBON DIOXIDE Application filed October 10, 19 27.- Serial No. 225,234

My invention pertains to the preservation of gaseous substances in a liquid condition and relates more specifically to an apparatus and process for the storing or transporting of liquid carbon dioxide.

To liquefy carbon dioxide it must be compressed to a pressure far above atmospheric, since at normal pressure it boils at 79 C. Liquid carbon dioxide has, in the past, been an expensive material to store or ship. The cost of vessels capable of withstanding'pressures of a thousand or more pounds per square inch is high. particularly for units of large capacity. The transportation cost of shipping these heavy vessels has likewise been quite high.

My present invention relates to an 1mproved process and apparatus for storing -hole (2). As iswell known to those skilled liquid carbondioxide at-a pressure much lower than thosepressures heretofore used. One of the advantages of my invention lies in the saving in"container cost which is made possible by the use of these lower pressures.

Another advantage resides in'the use of a portion of the material itself for autorefrigeration.'Otl1er advantages will become apparent. My invention is particularly useful in the shipping of liquid carbon dioxide by tank car or tank wagon.

Briefly, my invention comprises a vessel in which liquid carbon dioxide is kept at a pressure of only 100-300 pounds, evaporation of the material being greatly retarded by means of an insulationthrough which such portion of the carbon dioxide-as may be gasitied at that pressure is passed as a cold gas. My invention also contemplates a process'by which this desirable result is attained.

Suitable apparati for the practice of my invention are shown in the appended drawings.

In the drawings Figure 1 represents a longitudinal section of the tank, Figure 2 represents a transverse section of the tank taken througha a of Figure 1, and Figure 3 represents the same transverse section as shown in Figure 2 showing in addition the mounting of the tank on a railway carriage.

In Fig. 1, (1) is a cylindrical pressureresistant vessel of hammer-forged or'welded steel, capable of withstanding an internal pressure of at least 300 pounds per square inch. (1) is equipped with a dome manhole (2) which permits access to its interior. This manhole is ordinarily sealed by a cover (3). Liquid carbon dioxide may be placed in the vessel (1) through (3), by means of a pipe connection (4)" equipped with a suitable valve for closure and a threaded joint to permit the attachment of asupply pipe during the filling operation.

In the drawings the vessel (1) is shown to be about two-thirds full of liquid carbon dioxide. As was previously indicated it is desired to maintain this material under a pressure of 300 pounds per square inch. This purpose is accomplished by means of a pop valve (5) positioned within the dome manto regulate the pressure within the vessel 1). This pop valve is mounted on and dischargesthrough pipe (6) which penetrates the'manhole (2) as shown in the drawings.

Surrounding the vessel (1) there is a layer of porous insulating material (7) such as granular cork or granular sil-o-cel. This insulation'is supported by outer vessel (8), the insulation occupying the annular space between the vessels (1) and (8). The vessel (8) may also be made of suitable metal but may be of lighter construction, since it is not required to sustain an elevated pressure as in the case of vessel (1).

The pipe (6) supporting the pop valve (5) passes downward in the annular space between vessels (1) and (8) as shown in phantom in Fig. 1, and opens into the annular space filled with insulation (7) at orifice (9) The top of the outer vessel (8) is pro- I vided with an open vent The inner vessel (1) .is provided with a valve-controlled discharge pipe (11) In'Fig. 2, a cross-section of the apparatus is shown, this section being taken along the line aa' shown in Fig. l. The numerals used are the same in both drawings. In Fig.1

2, the course taken by thepipe (6) is clearly shown.

In the practice of my invention, liquid car bon dioxlde under a pressure of 300 pounds or more is passed into the vessel 1) through the connection (4) in the mannerprevious- 1y described. If the pressure at which the gas is admitted exceeds 300 pounds the excess .pressure is automatically relieved by the pop valve When the vessel has been filled to the desired heightthe connection (4) is closed.

As in the case of all other liquids, the boiling point of liquid carbon dioxide is directly proportional to the pressure. If the liquid carbon dioxide usedto fill the vessel is originally at a pressure much in excess of 300 pounds, the reduction in pressure during filling will tend to gasify some of the material, and this gas will also leave the vessel through the pop valve (5) as previously described. In any event, there will be a considerable gasification when the liquid first comes in contact with the vessel, since at 300 pounds pressure the liquid carbon dioxide will tend to boil at a temperature of about 20 0., and the vessel wlll be presumably at some normal climatic temperature much above 0 C. As a result, some of the liquid carbon dioxide will be gasified by the ab-.

sor tion of heat from the vessel and-this gas wili leave the vessel through the pop valve i rom the pop valve (5) the gaseous carbon dioxide is conveyed by pipe (6) downward through the insulation (72 within the annular space between vessels 1) and (8). The cold gas is discharged into the annular space through orifice (9). This cold gas permeates through the insulation (7) where 1t absorbs heat and gradually rises in the annular space, the upward motion being sus tained by the influx of further gas. The gas is discharged from the apparatus through vent (10). As the result of the vaporization of liquid within vessel 1) and the continued passa e of cold gas through the insulation] (7) t e temperature of the insulation and of the vessel (1) is gradually lowered so that eventually it ap roximates the tem rature of the carbon dioxide in vessel (1 -,i. e., 20 C. or less. v

The passage of the cold gaseous carbon dioxide through the annular space and through the interstices of the insulation (7 acts to abstract heat from these parts-and thus to reduce their temperature. When the apparatus reaches a lower heat-level than that of the surrounding air there is a transfer of heat from the air to the outer vessel (8). Some of this heat is absorbed by the cold gaseous carbon dioxide flowing in contact with the inner-wall of vessel (8). The insulation (7 in the annula'r space also serves to prevent the transfer of heat to the inner vessel (1) and in this respect it is about 40% more efiecti've'than it would be inan atmosphere of air'owing to the lower heat conductivity of carbon dioxide.

The apparatus containing the liquid carbon dioxide thus comes to an equilibrium at 300 pounds pressure and at this equilibrium the carbon dioxide itself and the inner vessel (1) are at a temperature below the boiling point of liquid carbon dioxide under the 300 pounds pressure. Since no insulation is perfectthere is inevitably some small quantity of heat transferred to the liquid and this heat willcause the gasification of more .liquid. The heat is absorbed by the carbon gasification loss fronr'a tank car to about 1- 1.5%,per twenty-ffoiit'hour period. In this manner, liquid carbon dioxide can be preserved during shipment in a cheap container at an expense which consists, merely, in a small evaporation loss.

As heretoforeiindicated,my invention is particularlyapplicable to the shipment of liquid carbondi'oxide in tank cars or tank wagons. The apparatus. shown in Figs. 1 and 2 is especially designed for this use and may be readily attached to the desired type of vehicle carriage. Since the liquid is contained in the inner vessel (1) the weight of the apparatusmust be transferredto the carriagefrom that point, rather than-from the outer vessel (8). v

In 3 a tank car for shipping-liquid carbon ioxide in accordance with my invention' is shown incross-section, the parts being numbered similarly to Figs-1 and 2. In Fig. 3, the apparatus is mounted on a railway carriage (12) by. means of support members fixed to the innervessel (1). Two such support members are shown in Fig. 3 as numerals.

' around vessel (8), forming a second annular space, and the gaseous carbon dioxide leaving vent (10) might discharge into this annular space and pass through it before reaching the outside air. This space might also be filled with insulation, as in the case of the space between vessels (1) and (8). Instead of placing the pop valve (5) within the dome manhole (2) it may be located within the annular space'between vessels (1) and (8). The pipe (6) conveying the gaseous carbon dioxide released by the valve (5) at a predetermined pressure might pass directly downward through the liquid in vessel and through the vessel itself, instead of 'would function in precisely the same man ner as was described in the specific example. The practical point involved is merely that it is most economicalto use the lowest storage pressure possible in order to reduce the thickness of the vessel (1) to a point where itcan be cheaply constructed; and to take advantage, as far as possible, of the autorcfzigera-tion caused by the gasification of the liquid carbon dioxide. Such a plan is to be pref'erred'rather than the old method of preserving the liquid carbon dioxide at extremelyihigh pressures without cooling. Also the use of a light apparatus reduces the basic cost of transportation.

lVhile 300 pounds was selected as the best operating pressure, pressures as low as 100 pounds may also be used with good results. Pressures below 100 pounds are not suitable for two reasons: first, because of the excessively thick insulation necessary to maintain the carbon dioxide at this low pressure without excessive evaporation; and second, on account of the danger of the freezing of the pop valve due to the formation of solid carbon dioxide. The freezing point of carbon dioxide is 57 C. and it is important that the gas discharged by the pop valve be well above this temperature, so that solidification will not take place at that point, with a resultant freezing and plugging of the valve which would tend to generate dangerous pressures within the vessel At 300 pounds pressure, the boiling point of liquid carbon dioxide is 19.5 C. and the cooling effect caused by the expansion to atmospheric pressure from this temperature is such that the final temperature of the gaseous carbon dioxide as it leaves the pop valve will be about '4r0 C. or well above the freezing point. At 100 pounds pressure the boiling point is about 46 C. and the temperature of the gas leaving the valve will be about 57 C. which is close to the freezing point.

While I have described my invention as suitable for preserving and transporting liquid carbon dioxide, it may likewise be employed for the shipment of other liquefied gases such as ammonia, methane, ethane, etc.

Now, having fully described my invention, I claim the following as new and novel Y 1. A container for liquefied gases comprising a pressure-resistant, liquid-containing vessel the walls of which have relatively high heat conductivity, an outer vessel vented to the atmosphere constructed of nonporous material surrounding the said liquid-containing vessel and forming an annular space therewith, a porous insulation in the space between said vessels, and in direct contact with the walls of the said liquid-containing vessel, and means for conveying the gases evolved in said liquid-containing vessel thru said space and insulation,'and in direct contact with the walls of the said liquid-containing vessel.

2. A container for liquefied gases, comprising a pressure-resistant, liquid-containing vessel the walls of which have relatively high heat conductivity, means for regulating the pressure within said vessel, an outer vessel vented to the atmosphere constructed of nonporous material surrounding the said liquidcontaining vessel and forming an annular space therewith, a porous insulation within said space, and in direct contact with the walls of said liquid-containing vessel. and means for conveying the gases evolved in said liquid-containing vessel thru said space, and in direct contact with the walls of the said liquid-containing vessel.

3. A container for liquefied gases comprising a pressure-resistant, liquid-containing vessel the walls of which have high heat conductivity, an outer vessel vented to the atmosphere constructed of non-porous material surrounding the said liquid-containing vessel and forming an annular space therewith, a porous insulation within said space and in direct contact with said walls, means for maintaining the liquefied gases at a predetermined pressure by releasing the gas generated at such pressure and means for passing the said released gas thru said space and in direct contact with the walls of said liquid-containing vessel.

4. A container for liquid carbon dioxide comprising a pressure-resistant, liquid-conreleasing the gas liberated at said pressure, and means for conveying said gas thru said space, and in direct contact with the Walls of said liquidrontaining vessel.

5 5. A container for liquid carbon dioxide comprising a pressure-resistant, liquid-containing vessel the Walls of which. have high heat conductivity, an outer Vessel vented to the atmosphere constructed of non-porous material and forming an annular space therewith, a porous insulation Within said space and in direct contact with said Walls, means for releasing gaseous carbon dioxide from said inner vessel at a pressure of about 300 pounds per square inch. and means for carryin; said released gas thru said space and'in direct contact with the walls of said space and in direct contact With the Walls of said li piid-eontainiu; vessel.

(l. The art of conserving liquefied gases which con'iprises maintaining the liquid at a predelermined adjustahle pressure above. atmospheric. whil ventingto the atmos phere thru a layer of porous insulation in thermal Contact with the liquid. the gas evolved at aid 1a'edetermined pressure.

T. The art t pl'vHQIW'lHQf liquid carhon dioxide at a predetermined adjustal le pressure at wh ch it would norinallv boil it e.\'

posed to the heat oi the atn'iosiiihere, which comprises venting to the atn'iosphere thru a porous. insulation in thermal contact with said liquid. the gas evolved at said piw'rdetermined pressure.

25 S. The art of preserving; liquid carhon dioxide which comprises maintaining it at a predciermined adjustable pressure in excess of 100 pounds per square inch while venting to the atmosphere thru a. layer of porous in- 40 snlation in ihern'ial Contact with the liquid,

the gas evolved at said predetermined pressure.

In testimony whereof I atlix my signature.

' WILLIAM .T. EDMONDS. 

